Improved fallow is a technology that can help to raise agricultural productivity in systems of poor soil fertility and low financial capital. Models, once calibrated, can be used to investigate a range of improved fallow systems relatively quickly and at relatively low cost, helping to direct experimental research towards promising areas of interest. Six fallow crop rotations were simulated using the WaNuLCAS model in a bimodal rainfall setting in Kenya over a 10 year period: (A) alternating fallow and crop seasons, (B) one season fallow followed by three seasons crop, (C) one season fallow followed by four seasons crop, (DF) 13 seasons fallow periods followed by 35 seasons cropThe strategies were tested using a number of fallow growth rates, soil clay contents, and rainfall amounts to determine the interaction of fallow rotation and biophysical vari- ables on maize (Zea mays (L.)) yield and sustainability (organic matter, N2 fixation, leaching). The best simulated fallow strategies doubled maize yield compared to continuous maize over a 10 year period. Across all biophysical treatments strategy A and B of no more than three consecutive cropping seasons and of one consecutive fallow season yielded the most maize. This was because fallow benefits were largely due to the immediate fallow soil fertility benefit (IFB) rather than the cumulative benefit (CFB). The difference in yield between the two strategies was through a balance between (1) their interaction with the biophysical variables affecting accumulation of organic matter, hence increasing soil fertility and (2) the extra intrinsic soil fertility used for maize productivity by the inclusion of more cropping seasons within the rotation. We propose the following conceptual framework to manage fallows for maximum maize yield: when environmental factors are strongly limiting to fallow and crop growth then fallow strategy A would be the best strategy to employ (less risk but more labour) and when factors are less limiting then strategy B would be the best to employ.
Tag: leaching
Benefiting from N2 -fixation and managing rhizobia
Nodulation and nitrogen fixation in the Leguminosae (Fabaceae) family, classification of rhizobia, and quantification of N2 fixed by different legumes are reviewed. Some promising management options intended to improve N2-fixation by direct selection of rhizobia in soil or by screening and breeding of legumes for increased N2-fixation, are discussed. The effects of pruning, soil phosphorus and pH, available nitrogen, and interactions of nematodes and rhizobia on nodulation and N2-fixation are analysed. The fate of fixed nitrogen can be determined by the recovery efficiency of N and leaching and gaseous N losses.